The present invention relates to dielectric ceramic compositions which exhibit high permittivity, small dependency of permittivity on temperature, small dielectric loss and, high dielectric breakdown voltage and a process for its production.
Ceramic capacitors with large capacity having a high rating DC voltage of 500 V and above are conventionally made from dielectric ceramic compositions containing a large percentage of barium titanate. However, such ceramic materials have serious disadvantages in that they exhibit large dielectric loss and large dependency of permittivity on voltage, and causes noises due to the piezoelectricity and the generation of large distortion of wave forms. In order to overcome these disadvantages, it has been proposed to use strontium titanate-based dielectric ceramic compositions, such as those containing bismuth titanate and lead titanate as additives, or those containing bismuth titanate and magnesium oxide as additives. However, these strontium titanate-based dielectric ceramic compositions, although exhibiting either small dielectric loss, small temperature change rate of permittivity or large permittivity, do not exhibit all these properties in combination. For example, the former exhibits large permittivity, but has disadvantages that it has large dielectric loss and large temperature change rate of permittivity. The latter may exhibit small dielectric loss of about 0.02% and small temperature change rate of permittivity of .+-.0%, but has the disadvantage that it exhibits low permittivity of about 1000.